This invention relates to mining devices and in particular to a new and useful coal planer conveyor in which the height of movement of the conveyor over the coal face may be varied.
A coal planer control serves the purpose of compensating for irregularities in the configuration of the floor of a longwall working area, or for deviations of the planer from the desired cutting horizon. To this end, the longwall conveyor is lifted or lowered by means of lifting cylinders which are provided at the waste side. In lowered position of the conveyor, the coal planer is positioned to "climb", while in the lifted position, the planer is positioned to "dip". As soon as the planer is positioned for a certain cutting horizon, the lifting cylinder occupies its neutral position and the piston rod is partly extended.
There is known a planer control mechanism in which the lifting cylinder is mounted in inclined position and hinged, by its piston rod end, to a control bracket in the upper portion thereof where a fixed hinge axis is thereby formed, and by its lower end to a control lever where a movable hinge axis is formed, with the control lever also forming an extension of a cross bar and being hinged to the lower portion of the bracket whereby another fixed hinge axis is formed. In this prior art design, due to the inclined position of the lifting cylinder, the movable hinge axis extends outside the bracket. The lifting cylinder thus extends in a relatively unprotected position, and, considering the normal position of the cylinder, the piston rod must be retracted if the planer is to be brought into a climbing position. Conversely, the piston rod must be extended if a dipping position of the planer is desired. Much greater setting forces must be produced to bring the planer into a climbing position, than for bringing it to a dipping position. Since in the prior art design, the climbing position is brought about by retracting the piston rod, just the piston surface, reduced by the cross section of the piston rod, is exposed to pressure to produce relatively high setting forces, while much smaller forces are needed for setting the dipping position. Taking into account a constant pressure of the operating fluid, the lifting cylinders thus must be dimensioned for the highest occurring setting, thus tensile forces, which requires a relatively large lifting cylinder which will be oversized in regard to the forces needed for the dipping position. In addition, in the prior art design the bottom edge of the waste side wall of the conveyor acts as a kind of a skid runner in the normal as well as in the climbing position of the planer, so that it tends to travel uphill on the coal dust cake forming on the floor, which also finally deviates the planer.
Further known is a control for a tearing hook-type planer which is equipped with a bottom sword extending below the conveyor and being secured at the waste side to the planer chain. The chain channels of the planer chain are formed by a U-shaped cover sheet which stands upright on the floor, yet does not project into the zone of the conveyor sidewall at the waste side. Therefore, during the shifting operation, fine coal may penetrate into, and deposit in, the lower chain channel. The movement may thereby be impeded, and even the chain may finally break.